What can be used to achieve desired application consistency in oil paint?

Using diluents is essential for achieving desired application consistency in oil paint. Diluents, often referred to as solvents, are substances that can be mixed with oil paints to alter their fluidity and thickness. They help to thin the paint, making it easier to apply, whether the goal is to create a smooth layer or to produce more transparent glazes. By adjusting the viscosity of the paint, artists can achieve different textures and effects, enhancing their control over the application process.

In contrast, water is typically not used with traditional oil paints, as oil and water do not mix effectively. Varnish is a finish applied on top of dried oil paint to enhance the appearance and provide protection, but it does not affect the application consistency of the paint itself. A binder is a component of the paint that holds the pigment particles together and adheres them to the painting surface, but it does not serve the purpose of altering consistency during application. Thus, diluents are specifically designed for modifying the consistency of oil paints, making them the correct choice for this question.